32 ARISAEMA TRIPHYLLUM 
distinct as reported by Rimbach for A. Dracontium. The mature 
roots show many branches near their tips (PLATE 5, FIG. 69). In- 
section these roots show a three- to five-radiate stele with a dis- 
tinct endodermis of one to two rows of thickwalled cells (PLATE 5, 
FIG. 66; TEXT FIG. 35). Around this is a thick cortex of paren- 
chymatous cells, small next to the endodermis but much larger and 
torn or distorted near the dark and more or less corky epidermis. 
As to the contractile feature of the roots of mature corms, 
the statement of Rimbach (24, p. 172) that the contraction may 
amount to 40 per cent. in the basal portion and a total of 
15 mm. or more for the whole root in A. Dracontium seems to hold 
equally well for A. triphyllum. The work of De Vries (8) and 
Rimbach (23) has left nothing to be added to this subject from a 
study of Arisaema. A point of interest appeared in the cutting 
of longitudinal sections of mature roots. The material had been 
killed in hot acetic alcohol and embedded in paraffin in the usual 
way. The transverse cortical ridges or wrinkles were quite 
prominent, but the stele seemed to be in normal position. As 
soon as the sections were cut, however, they became very much 
twisted and crumpled. Examination with the microscope showed 
the usual distortion of the outer cortical cells, an inner region of 
undisturbed cells, and then the stele section all twisted and 
folded (PLATE 5, FIG. 68), as though it had been held in position 
by the rigidity of the surrounding zone of cortical tissue. i 
The minute structure of a growing root tip of A. triphyllum 
shows a feature which seems unique. At the root tip (PLATE 5, 
FIG. 67) the usual angiosperm type is evident in the formation 
of a dermatogen, periblem, plerome, and root cap more sharply 
marked than in the onion. But at a point about the width of the 
root from the tip, there appear in the third and fourth layer of 
cells inside the dermatogen, large, elongating cells in every, way 
similar to those forming the primary xylem elements in the plerome 
(PLATE 5, FIGS. 63, 64, 65, 67). These cells increase in length and 
finally unite to form continuous tubes in the outer cortex of the 
root. Their walls remain unchanged and the cavities are at a 
very early period filled with bundles of raphides. 
